The invention is based on a fuel injection nozzle for internal combustion engines.
Because requirements made by engine manufacturers vary, contradictory tasks are often expected of a present-day Diesel fuel injection system, such as quiet operation, which is based on the longest possible injection duration, and good fuel preparation, which is attainable only with a short injection duration. While quiet operation is an object primarily during idling, so as to suppress the "dieseling" effect, better fuel preparation plays a role particularly in the upper rpm range, where the most important consideration is favorable fuel consumption. For this reason, depending on the use to which a given injection system is to be put, compromises are made in designing the components of a fuel injection system, such as the injection pump, the rpm governor and the injection nozzles. The introduction of electronics into Diesel fuel injection has made it easier to effect such compromises. Electronics are used above all in the Diesel governor, for which very precise measurements of the injection onset and duration are critical to the quality of regulation, and a satisfactory measurement can only be accomplished directly in the injection nozzle and via the valve needle. Certain injection functions, such as valve needle damping, are preferably accomplished by hydromechanical means, again in the injection nozzle. Because of the design specifications set by the manufacturers, however, an injection nozzle cannot be of arbitrarily large size; instead, whether with or without an electrical transducer and with or without damping, the injection nozzle should not exceed the dimensions of a conventional mass-produced nozzle, the size of which was taken into account by the engine designer in designing the engine. A further difficulty arises because electronics are used particularly in Diesel engines for passenger cars to make the smoothness of operation more nearly approach that of a vehicle powered by an Otto engine. In these passenger car engines, however, the fuel injection nozzles are relatively small because of the relatively low fuel consumption, and so some of the movable parts they contain are already a matter of precision engineering. Since the available space is already virtually optimally utilized for the basic structure of the passenger car injection nozzle, it is extremely difficult to accommodate additional damping devices or electrical transducers in the injection nozzle.
For reasons of space, the induction coil for the transducer of a known fuel injection nozzle (German Pat. No. 30 24 424.7) was placed in the vicinity of the nozzle holder, and the support ring that is moved with the valve needle was extended far enough beyond the end of the valve needle that it forms a magnetic circuit with the valve carrier and the nozzle holder. An unmagnetized spacer ring associated with the induction coil divides the induction coil from the support ring. In this realization, the external dimensions of the conventional, outwardly opening fuel injection nozzle of comparable capacity and in which no inductive transducer is disposed are not exceeded. In this known fuel injection nozzle, not only are there considerable transducer dissipation losses because of the relatively large volumes experiencing magnetic flux, but there is the further disadvantage that the remaining volume that is available for use is not sufficient to accommodate a damping device.